In recent years, many examples where a photonic crystal is applied to semiconductor lasers have been reported. Japanese Patent Application Laid-Open No. 2000-332351 describes a surface emitting laser light source in which an active layer containing a luminescent material is provided, and a two-dimensional photonic crystal is formed in the vicinity of the active layer. This is a sort of distributed feedback (DFB) laser. In this two-dimensional photonic crystal, cylindrical holes are periodically provided in a semiconductor layer, and so the refractive index distribution of the photonic crystal has two-dimensional periodicity.
Light generated in the active layer resonates due to this periodicity to form a standing wave to generate laser oscillation. In addition, the light is extracted in a direction perpendicular to the plane by primary diffraction to operate as a surface emitting laser.
In the above-described two-dimensional photonic crystal surface emitting laser, the resonated direction of the light is an in-plane direction, so that a part of the light leaks from the two-dimensional photonic crystal to the in-plane direction. Therefore, when laser devices are arranged in an array, crosstalk occurs between adjoining lasers.
Japanese Patent Application Laid-Open No. 2003-273460 discloses a structure for inhibiting the occurrence of such crosstalk.
In Japanese Patent Application Laid-Open No. 2003-273460, laser devices are arranged in a direction different from the light traveling direction in which the light travels (direction of the Poynting's vector), whereby crosstalk between adjoining lasers can be lessened.
According to this structure, however, while crosstalk in one certain direction can be lessened, but crosstalk in a direction perpendicular thereto cannot be lessened. Therefore, the structure is not suitable for such arrangement that the many laser devices that are two-dimensionally arranged.
On the other hand, when a reflection structure 10000 is provided between laser devices as illustrated in, for example, FIG. 6, crosstalk can be reduced, but return light 10020 occurs. In general, the return light affects the resonance mode of a DFB laser to make laser characteristics unstable.
A structure suitable for two-dimensional arrangement capable of reducing both crosstalk and return light at the same time has not yet been proposed.